The family of Johnny Hincapie with lawyer Ron Kuby after he filed a motion to overtun Hincapie's conviction. Photo: Steven Hirsch

It was a murder so shocking that it shook the already crime-ridden Big Apple to its core — and one of the seven convicted killers now claims he’s “the last victim.”

In court papers filed Monday, lawyers for jailbird Johnny Hincapie say he deserves a new trial over the 1990 slaying of Utah tourist Brian Watkins, who was stabbed in the heart as he tried to protect his parents from a gang of subway muggers.

Watkins, 22, was visiting New York City with his family on Labor Day weekend to attend the US Open tennis tournament when his parents were set upon by a pack of teens on the platform of the Seventh Avenue subway station at 53rd Street in Midtown on Sept. 3, 1990.

He was knifed when he stepped forward to help, and bled to death after collapsing near the token booth.

The horrific slaying — one of a record 2,245 homicides that year — galvanized the city, with an iconic New York Post front page imploring then-Mayor David Dinkins: “Dave, Do Something!”

Hincapie, 41, has already filed a series of failed appeals in the case, but now has “newly discovered evidence” that shows he “was not present when the mugging of the Watkins family occurred,” according to the Manhattan Supreme Court filing.

That evidence includes a sworn affidavit from a man who was cleared of taking part in Watkins’ murder and says Hincapie was elsewhere in the subway station at the time, the papers say.

Hincapie, who was convicted in 1991 and is serving 25 years to life, also alleges he was violently coerced into making a false confession.

Hincapie’s motion credits former newspaper reporter-turned-journalism professor Bill Hughes with discovering that co-defendant Luis Montero — against whom all charges were dismissed — was never questioned by cops regarding Hincapie and the Watkins murder.

In his affidavit, Montero says he was on the station’s upper level and saw Hincapie riding on an escalator when he heard screaming from the lower platform.